A radio communication system such as shown in FIG. 1 has been proposed as a radio communication system for carrying out processing of circuit switched calls in 3GPP (3rd Generation Partnership Projects).
The radio communication system shown in FIG. 1 is of a configuration in which UTRAN (Universal Terrestrial Radio Access Network) 10, which is a radio access network, is connected to CN (Core Network) 40.
MSC (Mobile-services Switching Center) 50 is provided in CN 40, and RNC (Radio Network Controller) 20 and Node-B (base station apparatus) 30 are provided in UTRAN 10. However, in some forms of UTRAN 10, the functions of RNC 20 are taken in by Node-B 30 and RNC 20 is not provided. Node-B 30 is connected to UE (User Equipment) 60, which is a radio communication apparatus, by way of a radio interface.
Circuit switched calls include AMR frames and AMR-WB frames that have been encoded by an AMR (Adaptive Multi-Rate) codec and AMR-WB (AMR Wideband) codec, and these AMR frames and AMR-WB frames have until now been transmitted and received on DCH (Dedicated Channels). The function of transmitting and receiving this type of circuit switched calls by a DCH is referred to as CS voice over DCH.
As shown in FIG. 2, the architecture of this CS voice over DCH uses an UL-DPDCH (Uplink Dedicated Physical Data Channel) on uplink lines and a DL-DPDCH (Downlink Dedicated Physical Data Channel) on downlink lines. In an entity referred to as MAC (Media Access Control)-d, ciphering (encryption and decryption) is implemented in AMR frames and AMR-WB frames. A method such as disclosed in Non-Patent Document 1 is used for the ciphering method.
Here, overall operations when establishing a radio access bearer (RAB) for a circuit switching domain (CS domain) on a DCH to realize a CS voice over DCH in a radio communication system are described with reference to FIG. 3.
In the following explanation, the radio access bearer for a circuit switching domain is referred to as simply a “radio access bearer.”
Explanation is presented on the assumption that messages transmitted and received between UE 60 and UTRAN 10 are RRC (Radio Resource Control) messages, and messages transmitted and received between UTRAN 10 and MSC 50 are RANAP (Radio Access Network Application Part) messages.
As shown in FIG. 3, an RRC connection is established between UE 60 and UTRAN 10 in state 1101 .
In Step 1102, MSC 50 next transmits to UTRAN 10 a RAB ASSIGNMENT REQUEST message instructing that a radio access bearer to DCH be established.
Next, in Step 1103, UTRAN 10 secures and sets DCH resources and uses a START value that was previously transmitted from UE 60 to implement ciphering configuration in the MAC. Here, the START value is an initial value used in the ciphering configuration of a circuit switched call. (For example, Non-Patent Document 2). In Step 1104, UTRAN 10 transmits a RADIO BEARER SETUP message including the information elements “RAB information for setup” instructing that a radio access bearer to DCH be established.
In Step 1105, UE 60 performs DCH settings that establish a DCH radio bearer in accordance with the instructions of the information elements “RAB information for setup” contained in the RADIO BEARER SETUP message that was received. In these DCH settings, both the setting of the START value and the ciphering configuration in the MAC that uses this START value are carried out. Still further, in Step 1106, UE 60 transmits to UTRAN 10 a RADIO BEARER SETUP COMPLETE message that includes the START value that was set.
UTRAN 10 subsequently, after using the START value that was transmitted from UE 60 to carry out updating of ciphering configuration in the MAC in Step 1107, transmits a RAB ASSIGNMENT RESPONSE message to MSC 50 in Step 1108.
Recently, however, a function referred to as “CS voice over HSPA” for transmitting and receiving AMR frames and AMR-WB frames by HSPA (High Speed Packet Access) was newly proposed in 3GPP RAN2 meeting #60 (Non-Patent Document 3). HSPA features higher transmission speed and higher frequency utilization efficiency than DCH.
In this CS voice over HSPA architecture, an E-DCH (Enhanced uplink DCH) is used on uplink lines and an HSDPA (High Speed Downlink Packet Access) that uses HS-DSCH is used on downlink lines, as shown in FIG. 4. In addition, as the ciphering of AMR frames and AMR-WB frames, encryption is carried out in an entity referred to as RLC UM TX (Radio Link Control Unacknowledged Mode Transmission)” and decryption is carried out in an entity referred to as RLC UM RX (RLC UM reception).
The overall operations when establishing a radio access bearer on an E-DCH/HSDPA to realize CS voice over HSPA in a radio communication system is here described with reference to FIG. 5.
As shown in FIG. 5, an RRC connection is first established between UE 60 and UTRAN 10 in state 1301.
In Step 1302, MSC 50 next transmits to UTRAN 10 a RAB ASSIGNMENT REQUEST message instructing the establishment of a radio access bearer on an E-DCH/HSDPA.
In Step 1303, UTRAN 10 secures and sets the E-DCH/HSDPA resources. In Step 1304, UTRAN 10 further transmits a RADIO BEARER SETUP message that includes the information elements “RAB information for setup” instructing the establishment of a radio access bearer on the E-DCH/HSDPA.
In Step 1305, UE 60 next carries out the E-DCH/HSDPA settings for establishing an E-DCH/HSDPA radio bearer in accordance with the “RAB information for setup” information element instructions contained in the RADIO BEARER SETUP message that was received. In these E-DCH/HSDPA settings, the setting of the START value and the ciphering configuration that use this START value are also carried out in RLC. Still further, in Step 1306, UE 60 transmits to UTRAN 10 a RADIO BEARER SETUP COMPLETE message including the START value that was set.
In Step 1307, UTRAN 10 then uses the START value that was transmitted from UE 60 to implement ciphering configuration in the RLC, and then, in Step 1308, transmits to MSC 50 a RAB ASSIGNMENT RESPONSE message.    Non-Patent Document 1: 3GPP TS 33.102 6.6.3 and 6.6.4    Non-Patent Document 2: 3GPP 25.331 V7.6.0, 10.3.3.38 and 8.5.9    Non-Patent Document 3: CHANGE REQUEST 25.331 CR CR3214